Hydraulic actuator



E. e. ATTEBO 3,425,218

\ HYDRAULIC ACTUATOR Filed July 20, 196'? fr'zz Er-z far" United States Patent 3,425,218 HYDRAULIC ACTUATOR Erik Gunnar Attebo, Saffle, Sweden, assignor to Aktiebolaget Kalle-Regulatorer, Saflle, Sweden Filed July 20, 1967, Ser. No. 654,903 Claims priority, applicatitgmggveden, Sept. 9, 1966,

US. CI. 60-52 6 Claims Int. Cl. F15b 15/26, 13/043; F04b 13/02 ABSTRACT OF THE DISCLOSURE BAOKGRO'UND OF THE INVENTION Field of the invention The invention relates to a pneumatically controlled hydraulic actuator system.

Description of the prior art In actuators of this type the pressure force acting on the piston within the hydraulic cylinder is primarily dependent on the size of the restricted outlet from the pressure side of the pump. Generally, the outlet has been dimensioned such that the pump has operated at the maximum pressure of -6 bars. If the pressure is increased by further throttling the outlet, a limit is fairly soon reached (about bars) where the air admixed in the pump liquid (oil) forms air cavities in the same way as in other rotary pumps, and this results in a poorer lubrication and consequently an increased wear.

Most of the previous actuators operating with gear wheel pumps have used one pump only to pull the piston of the servo cylinder against the action of a counterweight, and then a great deal of the pump pressure has been used for balancing the counter weight. The construction with two pumps mentioned above (Swedish Patent No. 194,307) involved the improvement that the counter-Weight could be dispensed with because the pumps drive two servo cylinders in opposite directions. In that way the whole pump force could be used for eifective work, but also in this case the fairly low maximum pump pressure mentioned above was considered as the only one practicable. However, a higher operating pressure is of great importance for obtaining a more rapid actuation and regulation.

SUMMARY OF THE INVENTION According to the invention, it has proved possible to i let the pumps operate at a considerably higher pressure of 30 bars or more, for instance, without any inconvenience arising, provided that the supply of gas to the pumps is entirely stopped before the dangerous pressures are established. If this is done, the lubrication becomes sufficiently eifective so that an abnormal wear is avoided. According to the invention, the pressure fluid conduits from the two pumps are each connected to one end of hydraulic servo cylinder common to both pumps and check valves in said conduits are arranged to open into the servo cylinder while overcoming a load such as a spring. Moreover, each of these check valves is adapted to be opened by a pressure responsive member actuated by the pressure in the conduit between the other valve and its pump.

3,425,218 Patented Feb. 4, 1969 Because the cylinder piston is driven by the pumps in both directions, no counter-weight is required, but the whole force acting on the piston can be utilized for regulation purposes. At the signal zero or when the pumps are inoperative, the piston is blocked in its adjusted position owing to the check valves provided in the pressure fluid conduits. When the two gas inlet valves receive a signal, the pressure will immediately be increased on the pressure side of the pump whose gas supply is throttled, but the piston is not actuated until the pressure has grown to such a magnitude that the loaded check valve in the pressure fluid conduit is opened. The device is designed such that the gas supply must be stoped almost entirely before the check valve opens, and thus the loaded pump will operate with an almost gas-free liquid, so that the pressure of the pump may be increased considerably by reducing the restricted outlet passage still further. It is true that with such a function the actuator will have a range of unresponsiveness around the zero value, but this is amply compensated by the fact that the increased control power causes an increased speed of regulation. On the other hand, said range of unresponsiveness can be made comparatively small by constructing the gas valves to move practically instantaneously from a wholly open into a wholly closed position already at a rather weak signal.

The invention will be described in more detail below with reference to the accompanying drawing which shows, diagrammatically, a vertical section through an embodiment of the actuator and its hydraulic cylinder.

The actuator is mounted in a housing of which only the lower part 1 is shown. Two equally large gear pumps 2 and 2' are adapted to be driven at the same speed by a. motor, not shown. The two pumps with their cooperating elements are identically alike so that only one of them need be described. At the suction side the pump 2 is connected to a pipe 3 extending downwardly into a quantity of oil contained in the housing, and said suction side is also connected to an air supply pipe 4 directed upwardly and having its inlet end controlled by a valve mechanism described below. The pressure side of the pump 2 is connected to a pipe 5 containing a restricted passage 6 and to a conduit 7 for the supply of pressure fluid to a valve housing 8.

The valve housing 8 contains three aligned chambers 9, 10, 11, between which there are central openings formed by annular seat members 12, 13. The conduit 7 ends in the middle chamber 10. One end chamber 9 contains a ball 14 normally kept pressed against the seat 12 by a spring 15 to serve as a valve member which interrupts the communication between the conduit 7 and a conduit 16 extending from the chamber 9. The other end chamber 11 is cylindrical and contains a movable piston 17. Its piston rod 18 extends through the middle chamber 10 towards the ball 14 and passes with clearance through the openings in the seat rings 12, 13. The rod 18 carries a valve member 19 within the middle chamber 10. At an overpressure in the conduit 7 the valve member 19 engages the seat ring 13 and blocks the connection between the chambers 10 and 11. A conduit 20 extending from the pressure fluid conduit 7 of the other pump 2' ends in the part of the cylinder chamber 11 located outside of the piston 17, and inside of the piston 17 the cylinder chamber 11 has an outlet opening 21. A similar conduit 20 connects the pressure conduit 7 to the lower end of the chamber 11'. Each of the conduits 20 and 20' has a branch conduit 23 and 23', respectively, provided with a restricted passage 22 and 22', respectively, and ending in a diaphragm box 24 and 24', respectively. Each diaphragm 25 and 25', respectively, is placed centrally in front of and slightly spaced from the orifice of the restricted outlet pipe 5 and 5', respectively, of the pump 2 and 2', respectively.

The pressure fluid conduits 16 and 16' extending from the valve housings 8 and 8, respectively, are each connected to one end of a hydraulic servo cylinder 26 containing a movable piston 27. The piston rod 28 is adapted to be connected to a controlling member in the customary way. To render possible a manual readjustment of the piston 27 when the actuator is idle, the ends of the cylinder 26 may be connected to conduits 29, 29' containing valves 30 and 30', respectively. One of said conduits 29, 29 may thus be connected to a hand-driven pump, while the other conduit is simply opened.

The valve mechanism controlling the supply of air to the suction pipes 4, 4 includes a balance arm 32 pivotably mounted in a support 31 and carrying valve plates 33, 33' at both ends. In their inoperative positions said valve plates 33, 33 are located slightly above the inlet ends of the tubes 4, 4, respectively. A rod 34 directed upwardly from the middle of the balance arm 32 is connected to a dip coil 35 enclosed by a permanent magnet 36. A conductor 37 connects the winding of the dip coil 35 to an electric pulse generator adjusted to emit, in an initial position (the signal zero), current of such intensity that the coil 35 keeps the arm 32 horizontal, both valves 33, 33' thus being open. When the current intensity is increased or reduced, the coil 35 will swing the arm 32 correspondingly so that one of the valve plates 33, 33 throttles its gas inlet. Preferably the arm 32 consists of a leaf spring which is bent by the suction power when a valve plate approaches its gas inlet. The valve plate is then quickly sucked onto the pipe orifice and stops the supply of gas completely. At a subsequent actuation of the arm 32 in the opposite direction, the valve plate is kept at the pipe orifice until the spring force becomes greater than the suction force, at which moment the plate is released suddenly and permits free passage for the gas. Thus, the resilient valve arm 32 contributes to an amplified signal and a quicker regulating operation.

The actuator described functions as follows. At the signal zero the piston 27 of the servo cylinder is locked in its adjusted position, as the valves 14, 14 in the pressure fluid conduits 7, 16 and 7', 16', respectively are closed when the gas valves 33, 33 are open, and consequently both pumps 2, 2 suck substantially air. Now, if an incoming signal swings the valve arm 32 anti-clockwise so that the valve 33 is closed and the pump 2 begins to suck oil only, the pressure increases in the conduit 7 and in the branch conduit 20 extending therefrom to the cylinder chamber 11. The piston 17 is then moved inwards so that the piston rod 18' lifts the valve ball 14 from its seat 12. Thus, the oil located in the right-hand chamber of the servo cylinder 26 is permitted to escape through the outlet opening 21 above the piston 17'. When the pressure in the conduit 7 and in the valve chamber has risen to such a value that it overcomes the action of the spring 15, the ball valve 14 is opened so that pressurized oil flows through the conduit 16 to the left-hand chamber of the servo cylinder 26, and the piston 27 is thus moved to the right.

The pressure in the conduit 20 is also transmitted to the diaphragm box 24 although with some delay owing to the restriction 22. When the diaphragm 25 is raised and closes the outlet opening of the pipe 5, the pump 2 gets an increased capacity for its continued operation.

As mentioned previously, the pumps may without any risk operate at a considerably higher pressure when the air supply is cut off. For instance, the restrictions 6, 6 in the outlets 5, 5 may be dimensioned for a pressure of 25-30 bars. When one of the outlets is closed by its diaphragm, the pressure rises further, and conveniently the pumps are dimensioned for a maximum pressure of 50-60 bars. I

When the required regulating operation has been carried out and the input signal again becomes zero, the previously closed air valve is opened so that both pumps run idly without load. Of course, this also contributes to a reduced wear. As soon as the pressure in the conduit 7 ceases, the check valves 14, 14 are closed and the piston 27 is then again locked in its position.

When the piston 27 of the servo cylinder approaches either end position it may be adapted to move, against the action of a spring, a valve spindle 38 or 38' introduced through the end wall of the cylinder. When moved, this spindle opens an air valve 39 or 39' mounted outside the cylinder and communicating through a conduit 40 or 40 with the air supply pipe 4 or 4. This arrangement ensures that a continued signal does not cause an operating pressure when the servo piston has been moved into its corresponding end position.

The pressure load may also become too great if the regulating member connected to the piston rod 28 is jammed and stops the piston 27 in an intermediate position during a regulating operation. To eliminate this risk, each pressure fluid conduit 16, 16' is by means of a branch conduit 41, 41 connected to a bourdon pipe 42, 42. The free end of each bourdon pipe 42, 42' carries a normally closed valve member in a valve 43, 43' which communicates with the air supply pipe 4, 4. When the pressure in the conduit 16 increases above a predetermined maximum, the bourdon pipe 42 is straightened and opens the valve 43 so that the pressure is released by supply of air to the pump 2.

Although the function of the regulator has been described primarily in connection with the operation of one of the pumps, pump 2, it is obvious that the other pump 2 and the details associated therewith function in a corresponding manner when the servo piston is moved in the opposite direction, i.e. to the left in the drawing.

The invention is not limited to the embodiment described above and shown in the drawing. For instance, the two check valves 14, 14' may be designed otherwise and the pistons 17, 17' actuating the check valves may be replaced by other pressure responsive means, such as diaphragms. Likewise, the diaphragrns 25, 25' and the bourdon pipes 42, 42' may be replaced by other pressure responsive means or be entirely omitted.

I claim:

1. A hydraulic actuator comprising two gear pumps each having an inlet for liquid and an inlet for gas on its suction side, valve members controlling said gas inlets and arranged to be actuated simultaneously in opposite directions by signal transmitting means so as to throttle the gas inlets alternately, a restricted outlet from the pressure side of each pump, a hydraulic servo cylinder adapted to perform a regulating operation, a pressure fluid conduit from the pressure side of one pump to one end of the cylinder, a pressure fluid conduit from the pressure side of the other pump to the other end of the cylinder, a first check valve in said first pressure fluid conduit and a second check valve in said second pressure fluid conduit, said check valves being arranged to open into the cylinder while overcoming a load (conveniently a spring), a pressure responsive member arranged to open the first check valve in dependence on the pressure in the conduit between the second check valve and its pump, and a pressure responsive member arranged to open the second check valve in dependence on the pressure in the conduit between the first check valve and its pump.

2. A hydraulic actuator as claimed in claim 1, in which the pressure fluid conduit between each pump and its check valve is also connected to another pressure responsive member arranged to close, With some delay, the restricted outlet of the pump.

3. A hydraulic actuator as claimed in claim 1, in which the valve members controlling the gas inlets are carried by the ends of a double-armed lever normally holding said members at a little distance from said inlets.

4. A hydraulic actuator as claimed in claim 3, in

which said lever is elastic to permit one of the valve members to move momentarily into closing position, when this valve member is subjected to a certain suction power from its gas inlet.

5. A hydraulic actuator as claimed in claim 1, in which the piston of the hydraulic servo cylinder is arranged, at the end of each stroke, to open a normally closed valve for supply of gas to the suction side of that pump which has caused said stroke of the piston.

6. A hydraulic actuator as claimed in claim 1, in which each pressure fluid conduit between its check valve and the servo cylinder is connected to a pressure responsive member arranged to open, at a pre-determined overpressure, a normally closed valve for supplying gas to the gas inlet of the pertaining pump.

References Cited UNITED STATES PATENTS 366,364 4/1943 Wiinsch et al. 2,356,597 8/ 1944 Kronenberger 6052 XR 2,942,581 6/1960 Gatfney 6052 3,031,846 5/1962 Wiegand 6052 EDGAR W. GEOGHEGAN, Primary Examiner.

US. Cl. X.R. 

